/*
 * Copyright 2002-2018 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.util;

import org.springframework.lang.Nullable;

/**
 * Helper class for resolving placeholders in texts. Usually applied to file paths.
 *
 * <p>A text may contain {@code ${...}} placeholders, to be resolved as system properties:
 * e.g. {@code ${user.dir}}. Default values can be supplied using the ":" separator
 * between key and value.
 *
 * @author Juergen Hoeller
 * @author Rob Harrop
 * @author Dave Syer
 * @see #PLACEHOLDER_PREFIX
 * @see #PLACEHOLDER_SUFFIX
 * @see System#getProperty(String)
 * @since 1.2.5
 */
public abstract class SystemPropertyUtils
{

    /** Prefix for system property placeholders: "${". */
    public static final String PLACEHOLDER_PREFIX = "${";

    /** Suffix for system property placeholders: "}". */
    public static final String PLACEHOLDER_SUFFIX = "}";

    /** Value separator for system property placeholders: ":". */
    public static final String VALUE_SEPARATOR = ":";


    private static final PropertyPlaceholderHelper strictHelper = new PropertyPlaceholderHelper(PLACEHOLDER_PREFIX, PLACEHOLDER_SUFFIX, VALUE_SEPARATOR, false);

    private static final PropertyPlaceholderHelper nonStrictHelper = new PropertyPlaceholderHelper(PLACEHOLDER_PREFIX, PLACEHOLDER_SUFFIX, VALUE_SEPARATOR,
            true);


    /**
     * Resolve {@code ${...}} placeholders in the given text, replacing them with
     * corresponding system property values.
     *
     * @param text the String to resolve
     * @return the resolved String
     * @throws IllegalArgumentException if there is an unresolvable placeholder
     * @see #PLACEHOLDER_PREFIX
     * @see #PLACEHOLDER_SUFFIX
     */
    public static String resolvePlaceholders(String text)
    {
        return resolvePlaceholders(text, false);
    }

    /**
     * Resolve {@code ${...}} placeholders in the given text, replacing them with
     * corresponding system property values. Unresolvable placeholders with no default
     * value are ignored and passed through unchanged if the flag is set to {@code true}.
     *
     * @param text                           the String to resolve
     * @param ignoreUnresolvablePlaceholders whether unresolved placeholders are to be ignored
     * @return the resolved String
     * @throws IllegalArgumentException if there is an unresolvable placeholder
     * @see #PLACEHOLDER_PREFIX
     * @see #PLACEHOLDER_SUFFIX
     * and the "ignoreUnresolvablePlaceholders" flag is {@code false}
     */
    public static String resolvePlaceholders(String text, boolean ignoreUnresolvablePlaceholders)
    {
        PropertyPlaceholderHelper helper = (ignoreUnresolvablePlaceholders ? nonStrictHelper : strictHelper);
        return helper.replacePlaceholders(text, new SystemPropertyPlaceholderResolver(text));
    }


    /**
     * PlaceholderResolver implementation that resolves against system properties
     * and system environment variables.
     */
    private static class SystemPropertyPlaceholderResolver implements PropertyPlaceholderHelper.PlaceholderResolver
    {

        private final String text;

        public SystemPropertyPlaceholderResolver(String text)
        {
            this.text = text;
        }

        @Override
        @Nullable
        public String resolvePlaceholder(String placeholderName)
        {
            try
            {
                String propVal = System.getProperty(placeholderName);
                if (propVal == null)
                {
                    // Fall back to searching the system environment.
                    propVal = System.getenv(placeholderName);
                }
                return propVal;
            }
            catch (Throwable ex)
            {
                System.err.println("Could not resolve placeholder '" + placeholderName + "' in [" + this.text + "] as system property: " + ex);
                return null;
            }
        }
    }

}
